1. Field of the Invention
This invention relates to a semiconductor device, and more particularly to a semiconductor device having an electrode covered with a protection film.
2. Description of the Related Art
In general, the entire surface of a semiconductor device is covered with a final protection film such as a plasma SiN film after the metal wiring layer and electrode layer are formed. A hole is formed in the final protection film to partly expose the electrode layer so that the exposed portion thereof can be used as a bonding pad section. An external package pin is connected to the bonding pad section by a bonding technique.
In the manufacturing process, charges tend to be accumulated on the surface of the final protection film, and an electric field of the intensity corresponding to the amount of accumulated charges is applied to the active region. In order to reduce the intensity of the electric field, it is necessary to form the final protection film sufficiently thick so as to separate the surface of the final protection film away from the active region, for example.
FIG. 1 is a cross sectional view showing the construction of a conventional MOS power transistor. The MOS transistor includes semiconductor substrate 1 of one conductivity type, semiconductor layer 2 of an opposite conductivity type, semiconductor layer 3 of the one conductivity type, gate insulation layer 5, conductive gate electrode layer 6, metal source electrode 7, metal gate electrode 8, metal drain electrode 9 and insulative protection film 10.
In the MOS transistor, the protection film is relatively thick. However, if insulative protection film 10 is patterned as shown in FIG. 1 to expose partial areas 7A and 8A of metal electrodes 7 and 8 so as to use partial areas 7A and 8A as bonding pad sections, the moisture resistance of bonding pad sections 7A and 8A will be lowered.
FIG. 2 is a cross sectional view showing the construction of a MOS transistor disclosed in Japanese Patent specification No. 62-10029. Portions which are the same as those in FIG. 1 are denoted by the same reference numerals. The MOS transistor further includes field insulation layer 4 and thin conductive film 11. This conductive film 11 is formed of a semiconductor region of a high impurity concentration or metal, and is used to improve the moisture resistance of bonding pad sections 7A. In this case, field protection film 4 has the same function as that of final protection film 10 obtained when it is formed thick.
However, formation of thin conductive film 11 and insulation layer 4 makes the construction complex and increases the number of manufacturing steps, thereby lowering the productivity of the semiconductor device.